Curable encapsulants and use thereof

ABSTRACT

The present invention relates to curable barrier encapsulants or sealants for electronic devices that have pressure sensitive adhesive properties. The encapsulants are especially suitable for organic electronic devices that require lower laminating temperature profiles. The encapsulant protects active organic/polymeric components within an organic electronic device from environmental elements, such as moisture and oxygen.

FIELD OF THE INVENTION

The present invention relates to curable barrier encapsulant or sealantfor electronic devices that have pressure sensitive adhesive properties.It is especially suitable for organic electronic device encapsulation.The encapsulant protects active organic or polymeric (hereinafterinterchangeably used) components within an organic electronic devicefrom environmental elements, such as moisture and oxygen.

BACKGROUND OF THE INVENTION

Organic electronic devices and circuits, such as, organic photovoltaics(OPV), organic light emitting diodes (OLED), organic electrophoreticdisplays, organic electrochromic displays, and the like, are becomingincreasingly prevalent in social and commercial uses. OLED, for example,have utility in virtual-view and direct-view displays, as lap-topcomputers, televisions, digital watches, telephones, pagers, cellulartelephones, calculators, large-area devices.

Various package geometries are known for organic electronic devices andcircuits, and in general, these geometries consist of an active organiccomponent disposed between a substrate/backsheet (hereinafterinterchangeably used) and a cover/frontsheet (hereinafterinterchangeably used), and the substrate and cover are adhered togetherwith a laminating adhesive or an encapsulant that encloses the activeorganic component. One or both of the substrate and the cover are madeof a transparent material, for example, transparent glass and flexiblethin plastic films. The active organic component is attached to thesubstrate, and in some embodiments, is covered with an inorganic barriercoating, a buffer film or a coating composed of an inorganic and/ororganic layer that seals the contact area between the component and thesubstrate at its perimeter. An encapsulant is applied over the activeorganic component, and over the barrier coating, when present. Thisencapsulant fills the space between the substrate and the cover,encloses the active organic component and adheres the substrate to thecover. In some embodiments, a desiccant package, in the form of a pouch,or a thin or thick film, is attached to the cover, usually in anindentation or cavity in the cover, or alternatively, the desiccant isprovided in grooves within the cover.

Most active organic components within organic electronic devices aresusceptible to degradation by moisture and oxygen. For example, an OLED,simply described, consists of an anode, a light emitting layer, and acathode. A layer of a low work function metal is typically utilized asthe cathode to ensure efficient electron injection and low operatingvoltages. Low work function metals are chemically reactive with oxygenand moisture, and such reactions will limit the lifetime of the devices.Oxygen and moisture will also react with the light emitting organicmaterials and inhibit light emission. Therefore, the packagessurrounding the active organic components are designed to restricttransmission of both oxygen and water vapor from the environment to theactive organic components.

An encapsulant with pressure sensitive adhesive properties can be usedto restrict transmission of oxygen and water vapors, and the pressuresensitive adhesive is typically provided in a thin film between twosilicone release carrier films (liners) as an encapsulant film. Uponremoval of one of the liners, the exposed encapsulant film is attachedto either the cover or the substrate of the device. Subsequently, thesecond liner is removed, allowing the cover and the substrate to belaminated (or attached) to one another. The encapsulant film mustmaintain adhesion and flexibility upon long term exposure to strain.

An encapsulant film or encapsulant (hereinafter interchangeably used)with pressure sensitive adhesive properties can facilitate manufacturingthrough-put of the device. While manufacturing speed and toxicity areimproved for encapsulant with pressure sensitive adhesive properties,drawbacks include poor wet out and void formation during assemblybecause films typically have higher viscosity than their liquidencapsulant counterparts at assembly temperatures. This problem isexacerbated for substrate that contains components such as, electrodes,bus bars, ink steps, integrated circuits, wires, and the like, due totheir irregular surfaces. In order to obtain better wet out and tominimize the formation of voids, hot lamination is usually applied tothe uncured encapsulant film. However, organic components are sensitiveto heat and prolonged exposure to heat is detrimental to the components.Also, because the encapsulants are pressure sensitive adhesive film, thefilm must maintain minimal cold flow at room temperature duringprolonged storage.

WO 2009/148722 and WO 2011/062932 disclose the use of high (typicallygreater than 300,000 Da) weight average molecular weight (Mw)polyisobutylene-based encapsulants. Such encapsulants yield pressuresensitive adhesive films having high viscosity, and thus are susceptibleto voids or air bubbles in organic electronic devices. While applicationtemperature can be increased to minimize this problem, active organiccomponents start to decompose at about 120° C. Moreover, encapsulantsmade from such high Mw are formed by solution casting, and are notextruded as hot melts, unless extreme temperatures and pressure can beutilized.

JP2012057065 discloses non-curable encapsulants with pressure sensitiveadhesive properties. In order to properly wet the substrates withcomponents and to minimize void formations, the viscosity of theencapsulant film must be kept below 1,000,000 cps or below 200,000 Daviscosity average molecular weight (Mv) at 120° C. Furthermore, thethermal plastic encapsulant exhibits cold flow under strain during thelifetime of the device.

Therefore, there is a need in the art for a curable encapsulant filmthat can laminate at temperatures below 120° C., maintain good adhesion,wet-out on the substrates with irregular surface, minimize cold flow,and form a void-free encapsulation while allowing for flexibility of thesubstrates over long term exposure to strain. The current inventionfulfills this need.

BRIEF SUMMARY OF THE INVENTION

The invention provides radiation or heat curable encapsulants suitablefor sealing and adhering substrates and covers of organic electronicdevices to protect the active organic components of the device frommoisture and oxygen. The radiation or heat curable encapsulants havepressure sensitive properties which allow the devices to maintainflexibility and creep resistance upon long term exposure to strain. Theencapsulants comprise a barrier rubber, a radiation or heat reactivebarrier resin, and a radical initiator. The encapsulants may furthercomprise a diluent, wax, antioxidant, and/or desiccant fillers.

In one embodiment, the curable encapsulant comprises:

-   -   (a) a polyisobutylene (PIB) having a Mw of from about 1,000 to        about 95,000 Da;    -   (b) a functionalized polyisobutylene having (i) a Mw (weight        average molecular weight) of from about 1,000 to about 95,000 Da        and (ii) greater than one free-radical reactive functional        group, wherein the free-radical reactive functional group is        selected from the group consisting of terminal (meth)acrylates,        pendant (meth)acrylates, terminal acrylates, and/or pendant        acrylates; and    -   (c) a radical initiator.        The encapsulant is essentially free of any acrylic monomer with        Mw less than about 1,000 Da or volatile organic compound with Mw        less than about 1,000 Da, and the encapsulant is essentially        free of a tackifier. The term “essentially free of,” herein,        indicates that the encapsulant contains less than 5,000 ppm        (parts-per-million) based on the entire encapsulant composition.        The curable encapsulant may further comprise of a functionalized        polyolefin having (i) a Mw of from about 1,000 to about 95,000        Da and (ii) the functionalized polyisobutylene contains greater        than 1 free-radical reactive functional group, wherein the        free-radical reactive functional group is selected from the        group consisting of terminal (meth)acrylates, pendant        (meth)acrylates, terminal acrylates, and/or pendant acrylates.

In another embodiment, the curable encapsulant comprises:

-   -   (a) a polyisobutylene having a Mw of from about 1,000 to about        95,000 Da;    -   (b) a functionalized polyolefin having (i) a Mw of from about        1,000 to about 95,000 Da and (ii) greater than 1 free-radical        reactive functional group, wherein the free-radical reactive        functional group is selected from the group consisting of        terminal (meth)acrylates, pendant (meth)acrylates, terminal        acrylates, and/or pendant acrylates; and    -   (c) a radical initiator.        The encapsulant is essentially free of any acrylic monomer with        Mw less than about 1,000 Da or volatile organic compound with Mw        less than about 1,000 Da, and the encapsulant is essentially        free of a tackifier.

In a further embodiment, the curable encapsulant comprises:

-   -   (a) an amorphous polyalphaolefin having a Brookfield viscosity        less than 8,000 cps at 190° C.    -   (b) a functionalized polyolefin having (i) a Mw of from about        1,000 to about 95,000 Da and (ii) the functionalized        polyisobutylene contains greater than 1 free-radical reactive        functional group, wherein the free-radical reactive functional        group is selected from the group consisting of terminal        (meth)acrylates, pendant (meth)acrylates, terminal acrylates,        and/or pendant acrylates; and    -   (c) a radical initiator; and    -   (d) a tackifier.        The encapsulant is essentially free of an acrylic monomer with        Mw less than about 1,000 Da or volatile organic compound with Mw        less than about 1,000 Da.

For the above curable encapsulants, the radical initiator is selectedfrom the group consisting of photoinitiator and thermal initiators.Curable encapsulants with photoinitiators are typically formed as hotmelts, and the Brookfield viscosity of the encapsulant ranges from about10,000 to about 900,000 cps at 130° C. Curable encapsulants with thermalinitiators are typically solution cast, and the Brookfield viscosity ofthe encapsulant ranges from about 10,000 to about 900,000 cps at 80° C.

In another embodiment, the curable encapsulant is formed by combiningthe above described components of the encapsulants at 80° C. to about150° C. until a homogeneous melt is formed, extruding or casting themelt to a thickness of about 0.01 to about 10 mm film, and cooling thefilm.

Yet in another embodiment, the curable encapsulant is formed bycombining the above described components of the encapsulants with asolvent at room temperature until a homogeneous mixture is formed,casting the mixture to a thickness of about 0.01 to about 10 mm film,and evaporating or driving off the solvent.

Another embodiment is directed to a process for forming a curedencapsulant device comprising the steps of:

-   -   (1) applying above described curable encapsulants onto at least        a portion of a substrate at a temperature of from about 50 to        about 120° C.;    -   (2) applying a cover onto the curable encapsulant; and    -   (3) curing the curable encapsulant    -   whereby the encapsulant cures and adheres the substrate to the        cover.        Curing the curable encapsulant is conducted by UV irradiation        and/or thermal radiation. In another embodiment, the curable        encapsulant is first applied onto the cover in step (1), and the        substrate is applied onto the curable encapsulant at step (3).

Yet another embodiment is directed to devices comprising the abovedescribed cured encapsulant. Devices include electronic, optoelectronic,OLED, photovoltaic cells, organic photovoltaic cells, flexible thin filmorganic photovoltaic cells, CIGS photovoltaic cells, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a Brookfield viscosity curve.

DETAILED DESCRIPTION OF THE INVENTION

All references cited herein are incorporated in their entirety byreference.

The term radiation cure herein refers to toughening, hardening orvulcanization of the curable portion of the encapsulant through actinicradiation exposure. Actinic radiation is electromagnetic radiation thatinduces a chemical change in a material, and for purposes within thisspecification and claims will include electron-beam curing. In mostcases, such radiation is ultraviolet (UV) or visible light. Theinitiation of this cure is achieved through the addition of anappropriate photoinitiator. The cure of the encapsulant is achieved bydirect exposure to ultraviolet (UV) or visible light or by indirectexposure through transparent lid or cover sheet that are made ofpolyester, polycarbonate, glass, and the like.

The term heat cure refers to toughening, hardening or vulcanization ofthe curable portion of the encapsulant through exposure to heat in oven,infrared (IR), near IR, or microwave. The heat cure temperature isbetween 50-200° C., preferably 100-170° C.

Polyisobutylenes (PIB) and PIB diluents are substantially homopolymersof isobutylene. They can also be called polybutene and butyl rubbers.They usually contain less than 75% terminal alpha olefins per polymerchain. The PIB and PIB diluents are free of any other radical reactivefunctional groups including, but are not limited to, acrylate,(meth)acrylate, styrenic C═C bonds, diallyl, maleic anhydride, and thelike. Commercially available PIB and PIB diluents include, but not limitto, Oppanol, Glissopal, and Indopol. While many of these PIB may containeven up to 75% terminal alpha C═C bonds, the reactivity of these PIBtowards free radical reaction are relatively low and incomplete, and aretherefore considered to be non-reactive or non-curable RIB. Moreover,the weight average molecular weight (Mw) of the PIB and PIB diluentsranges from about 1,000 to about 95,000 Da. PIB diluents typically havea Mw ranging from about 1,000 to about 10,000 Da. These low Mw and lowviscosity PIB polymers are preferred in the encapsulant to achieve 100%wet out and coatable hot melts.

PIB in the curable encapsulant is in the amount ranging from about 10 toabout 90 weight percent, more preferably from about 70-90 weightpercent, based on the total weight of the curable encapsulant, withoutaccounting for any solvents.

Exemplary amorphous polyalphaolefin (APAO) include polymers of randomcopolymers or terpolymers of ethylene, propylene, and butene, and othersubstantially amorphous or semicrystalline polymers. Suitably, the APAOincludes between about 20% and about 80% copolymers or terpolymers andbetween about 20% and about 80% other substantially amorphous orsemi-crystalline propylene-ethylene polymers. Alternatively the APAOincludes between about 40% and about 60% copolymers or terpolymers andbetween about 40% and about 60% other substantially amorphous orsemi-crystalline propylene-ethylene polymers. APAO may be a 1-butenecopolymer with ethylene or propylene, or a 1-butene terpolymer withethylene and propylene, having a Brookfiled viscosity less than 8,000cps at 190° C. The 1-butene copolymer should include about 20% to about65% by weight 1-butene, or about 30% to about 55% by weight 1-butene.Alternatively, the APAO may include an ethylene-propylene copolymerhaving up to 80% ethylene. Commercially suitable APAO includes Rextac(Rexene LLC), Eastoflex (Eastman Corporation), Vestoplast (EvonikCorporation). Suitable APAO has a viscosity less than 8,000 cps at 190°C. Metallocene catalyzed semicrystalline polyolefin with melting pointless than about 100° C. can also be suitable in the curable encapsulantand replace APAO which uses Ziegler Natta catalyst. Exemplary lowmelting point semicrystalline polyolefins includes C2-C6 polyolefins,which have weight average molecular weight less than about 100,000 Daand polydispersity index less than about 3. These low melting pointsemicrystalline polyolefins are commercially available from Exxon Mobilas Linxar series.

APAO in the curable encapsulant is in the amount ranging from about 10to about 90 weight percent, more preferably from about 70-90 weightpercent, based on the total weight of the curable encapsulant, withoutaccounting for any solvent.

Exemplary functionalized PIB includes, but are not limited to, diallylpolyisobutylene, di(meth)acrylate polyisobutylene, and vinyl-terminalpolyisobutylene. Representative polyisobutylene (meth)acrylate aredescribed in U.S. Pat. No. 5,171,760 issued to Edison Polymer InnovationCorp., U.S. Pat. No. 5,665,823 issued to Dow Corning Corp., and PolymerBulletin, Vol. 6, pp. 135-141 (1981), T. P. Liao and J. P. Kennedy.Representative polyisobutylene vinyl ethers are described in PolymerBulletin, Vol. 25, pp. 633 (1991), J. P. Kennedy, and in U.S. Pat. Nos.6,054,549, 6,706,779B2 issued to Dow Corning Corp. Preferredfunctionalized PIB is a free radical reactive polyisobutylene, butylrubber derivatives, and like, which are terminated or grafted with(meth)acrylic or 75% of alpha-olefin functional groups. Particularly,the functionalized polyisobutylene has (i) a Mw of from about 1,000 toabout 95,000 Da and (ii) contains greater than one free-radical reactivefunctional group per polymer chain. The functionalized PIB is formedwith free-radical functional group selected from terminal(meth)acrylates, pendant (meth)acrylates, terminal acrylates, and/orpendant acrylates.

Functionalized polyolefin in the invention includes free radicalreactive (meth)acrylic terminal and grafted pendant functionaloligomers, polymers, or random copolymers of butadiene, isoprene,ethylene, propylene, butene and derivatives. The functionalizedpolyolefin has a Mw from about 1,000 to about 95,000 Da and containsgreater than one free-radical reactive functional group in the polymerchain. The functionalized polyolefin is formed with free-radicalfunctional group is selected from terminal (meth)acrylates, pendant(meth)acrylates, terminal acrylates, and/or pendant acrylates. Thefunctionalized olefin is formed with free-radical functional group isselected from terminal (meth)acrylates, pendant (meth)acrylates,terminal acrylates, and/or pendant acrylates. Exemplary functionalizedoligomers, polymers or copolymers include, but are not limited to,di(meth)acrylated-polybutadienes, di(meth)acrylated-polyisoprenes,hydrogenated di(meth)acrylated-polybutadienes, hydrogenateddi(meth)acrylated-polyisoprenes, many of which are available fromSartomer and Kuraray. “(Meth)acrylated” is defined herein as beingfunctionalized with either acrylate or methacrylate. In otherembodiments, other reactive liquid oligomers and/or polymers that are(meth)acrylated and can be partially used to replace the curablefunctional polyolefin, and they include, but are not limited to,(meth)acrylated-polyurethanes, (meth)acrylated urethane oligomers, and(meth)acrylated-polyesters, (meth)acrylated styrene-butadiene copolymer,(meth)acrylated acrylonitrile-butadiene copolymer, (meth)acrylatedpolysiloxanes, (meth)acrylated EPDM rubber (ethylene propylene dienecopolymer), (meth)acrylated butyl rubber, (meth)acrylated bromobutylrubber (bromoisobutylene-isoprene copolymer), (meth)acrylatedchlorobutyl rubber (chloroisobutylene-isoprene copolymer. These resinsare commercially available without the (meth)acrylate functionality andcan be functionalized without undue experimentation by those skilled inthe art.

Functionalized PIB in the curable encapsulant is in the amount rangingfrom about 5 to about 90 weight percent, more preferably from about10-50 weight percent, based on the total weight of the curableencapsulant, without accounting for any solvent.

Examples of terminal and/or grafted pendant functionalities that arereactive and curable by radiation or heat in the reactive PIB or thereactive polyolefin include, but are not limited to, those selected fromthe groups consisting of acrylate, methacrylate, vinyl, vinyl ether,propenyl, crotyl, allyl, silicon-hydride, vinylsilyl, propargyl,cycloalkenyl, thiol, glycidyl, aliphatic epoxy, cycloaliphatic epoxy,oxetane, itaconate, maleimide, maleate, fumarate, cinnamate esters,styrenic, acrylamide, methacrylamide, and chalcone groups.

The radical cure initiator includes a radical polymerization initiatorthat generates radicals by being decomposed by electromagnetic energyrays such as UV rays, or a thermally decomposable radical initiator thatgenerates radicals by being thermally decomposed. Radicalphotopolymerization initiating system comprising one or morephotoinitiators can be found in Fouassier, J-P., Photoinitiation,Photopolymerization and Photocuring Fundamentals and Applications 1995,Hanser/Gardner Publications, Inc., New York, N.Y.

The radical photopolymerization initiators include Type I alpha cleavageinitiators such as acetophenone derivatives such as2-hydroxy-2-methylpropiophenone and 1-hydroxycyclohexyl phenyl ketone;acylphosphine oxide derivatives such as bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; and benzoin ether derivatives such as benzoinmethyl ether and benzoin ethyl ether. Commercially available radicalphotoinitiators include Irgacure 651, Irgacure 184, Irgacure 907,Darocur 1173 and Irgacure 819 from Ciba Speciality Chemical. Type IIphotointiators are also suitable for the curable encapsulant, and theyinclude benzophenone, isopropylthioxanthone, and anthroquinone. Manysubstituted derivatives of the aforementioned compounds may also beused. The selection of a photoinitiator for the radiation curableencapsulant is familiar to those skilled in the art of radiation curing.The photoinitiator system will comprise one or more photoinitiators andoptionally one or more photosensitizers. The selection of an appropriatephotoinitiator is highly dependent on the specific application in whichthe encapsulant is to be used. A suitable photoinitiator is one thatexhibits a light absorption spectrum that is distinct from that of theresins, and other additives in the encapsulant. The amount of thephotoinitiator is typically is in a range of about 0.01 to about 10 wt%, preferably, from about 0.01 to about 5 wt %, based on the totalweight of the encapsulant, without accounting for solvent.

In one embodiment, the encapsulant is cured through an optical clearcover or frontsheet, the photoinitiator must be capable of absorbingradiation at wavelengths for which the cover or substrate istransparent. For example, if an encapsulant is to be cured through asodalime glass coverplate, the photoinitiator must have significant UVabsorbance above 320 nm. UV radiation below 320 nm will be absorbed bythe sodalime glass coverplate and not reach the photoinitiator. In thisexample, it would be beneficial to include a red shifted photoinitiatoror a photosensitizer with the photoinitiator into the photoinitiatingsystem, to augment the transfer of energy to the photoinitiator. If anencapsulant is to be cured through a barrier PET film with cut offabsorbance below 400 nm, the photoinitiator must have UV absorbanceabove 400 nm. Examples of such photointiators include, but are notlimited to, Irgacure® 819, Irgacure® 2022, Lucirin TPO or TPO-L, whichare commercially available from BASF.

The thermally curable radical polymerization initiators includeperoxides, such as, 1,1,3,3-tetramethylbutyl peroxy-2-ethyl-hexanoate,1,1-bis(t-butylperoxy) cyclohexane,1,1-bis(t-butylperoxy)cyclo-dodecane, di-t-butyl peroxyisophthalate,t-butyl peroxybenzoate, dicumyl peroxide, t-butyl cumyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy) hexane,2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne and cumene hydroperoxide.The amount of the radical thermal initiator is typically is in a rangeof about 0.01 to about 10 wt %, based on the total weight of theencapsulant, without accounting for solvent.

In one embodiment, the thermal-curing initiator is desirably selected toprovide a moderate initiation temperature, which is high enough toprevent premature cross-linking, but also low enough to prevent exposingelectronic devices to excess temperatures. Such excess temperatures maydegrade the reactive organic components within the devices. Examples ofsuitable commercially available free radical thermal initiator include,but are not limited to, LUPEROX TBEC from United Initiators, TRIGONOX101 and TRIGONOX 201 from Akzo Nobel Polymer Chemicals, LUPEROX 101 andLUPEROX 231 from Arkema, DICUP from GEO Specialty Chemicals,2,5,-Dimethyl-2,5 BIS (Tert-Butyl Peroxy) Hexyne-3, such as thoseavailable under the trade designation LUPEROX 130 from Arkema, TRIGONOX145 from Akzo Nobel Polymer Chemicals; Di-Tert-Butyl Peroxide such asthose available under the trade designation TRIGONOX B from Akzo NobelPolymer Chemicals. Suitable amounts of thermal free radical initiatorsrange from about 0.01 to about 10 wt %, based on the total weight of theencapsulant, without accounting for solvent. Typical cure temperaturesfor these free radical initiators typically range from about 130 toabout 200° C., but temperatures can be increased for faster cures.

In some embodiment, inorganic fillers may be used to improve themoisture and oxygen barrier properties of the encapsulant.Representative fillers include, but are not limited to, ground quartz,fused silica, amorphous silica, talc, glass beads, graphite, carbonblack, alumina, clays, grapheme, nanoclay, mica, aluminum nitride, andboron nitride. Metal powders and flakes consisting of silver, copper,gold, tin, tin/lead alloys, and other alloys also are suitable fillersfor conductive applications. Organic filler powders such aspoly-(tetrachloro-ethylene), poly(chlorotrifluoroethylene),poly(vinylidene chloride) may also be used. The type and amount of suchfillers suitable for use in radical-curable encapsulant is within theexpertise of the practitioner skilled in the art. Generally, however,such fillers will be present in amounts ranging from 0.5 to 50 wt % ofthe total encapsulant, without accounting for solvent.

In a further embodiment, desiccant may be used to improve the moisturebarrier properties of the encapsulant. When added, desiccant comprise upto 20 wt % of the encapsulant, not including the solvent. The fillerswith desiccant properties (referred to as desiccant fillers) suitablefor use may be any of those that provide an appropriate moisturescavenging rate, capacity, and residual moisture level (the lowest levelof moisture at which the desiccant can actively scavenge water) to meetthe allowable moisture level for the specific electronic device. Thedesiccant fillers will be capable of reacting with, absorbing, oradsorbing water and/or water vapor. A representative list of suchdesiccants can be found in Dean, J. Lange's Handbook of Chemistry, 1999,McGraw Hill, Inc., New York, N.Y., pp. 11.5.

In general, suitable desiccants include metal oxides, such as, CaO, BaO,MgO; other oxides, such as SiO₂, P₂O₅, Al₂O₃; metal hydrides, such asCaH₂, NaH, LiAlH₄; metal salts, such as CaSO₄, Na₂SO₄, MgSO₄, CaCO₃,K₂CO₃, and CaCl₂; powdered zeolites, such as 4 A and 3 A molecularsieves; metal perchlorates, such as, Ba(ClO₄)₂, Mg(ClO₄)₂;superabsorbant polymers, such as, lightly cross linked poly(acrylicacid); and metals that react with water, such as calcium. As with anyfiller, the desiccant filler particle size, particle size distribution,shape, and surface functionality will affect the level to which it canbe loaded into a resin system and what rheology may result. Such factorsare understood by those skilled in the art and are not otherwiserelevant to the current inventive compositions. Blends of the morecommon non-desiccant fillers disclosed above and these desiccant fillersare contemplated and described within the examples. A common range forthe particle size of the desiccant filler is from about 0.001 to about200 micrometers. The practitioner with skill in the art will be able todetermine the appropriate particle size range for the resin, rheology,and scavenging rate needed for the particular end use application.

The encapsulant may further comprise plasticizers, tackifier, wax, andmineral oil to adjust the viscosity of the formulations.

A non-limiting example of a plasticizer includes polar plasticizer,solid plasticizer, liquid plasticizer (natural and synthetic), andplasticizer that is primarily aliphatic in character and is compatiblewith PIB and polyolefins. Solid plasticizer is a solid at ambienttemperature, and preferably has a softening point above 60° C. Any solidplasticizer that is able to subsequently recrystalize in the encapsulantis suitable. Examples include 1,4-cyclohexane dimethanol dibenzoate,Benzoflex 352, available from Genovique Specialties. A non-limitingexample of a natural liquid plasticizer is a vegetable oil. Syntheticliquid plasticizers include liquid polyolefins, iso-paraffins orparaffins of moderate to high molecular weight. Examples includeSpectraSyn Plus 6 from ExxonMobil Chemical. Exemplary liquid tackfiers(having a Ring and Ball softening point below about 25° C.) are liquidtackifying diluents that include polyterpenes such as Wingtack 10available from Sartomer, and Escorez 2520 available from ExxonMobilChemical. The synthetic liquid oligomers are high viscosity oligomers ofpolybutene, polypropene, polyterpene, and etc., which are permanently inthe form of a fluid. Examples include polyisoprene, available as LIR 50from Kuraray, and Amoco's polybutenes available under the name Indopol,Wingtack 10 from Sartomer and synthetic liquid oligomer polybutenes suchas Indopol 300 from Amoco.

Suitable tackifiers include, but are not limited to, any resins ormixtures compatible to PIB or polyolefins thereof such as (1) natural ormodified rosins such, for example, as gum rosin, wood rosin, tall oilrosin, distilled rosin, hydrogenated rosin, dimerized rosin, andpolymerized rosin; (2) glycerol and pentaerythritol esters of natural ormodified rosins, such, for example as the glycerol ester of pale, woodrosin, the glycerol ester of hydrogenated rosin, the glycerol ester ofpolymerized rosin, the pentaerythritol ester of hydrogenated rosin, andthe phenolic-modified pentaerythritol ester of rosin; (3) copolymers andterpolymers of natural terpenes, e.g., styrene/terpene and D-methylstyrene/terpene; (4) polyterpene resins having a softening point, asdetermined by ASTM method E28,58T, of from about 80 to about 150° C.;the latter polyterpene resins generally resulting from thepolymerization of terpene hydrocarbons, such as the bicyclic monoterpeneknown as pinene, in the presence of Friedel-Crafts catalysts atmoderately low temperatures; also included are the hydrogenatedpolyterpene resins; (5) phenolic modified terpene resins andhydrogenated derivatives thereof, for example, as the resin productresulting from the condensation, in an acidic medium, of a bicyclicterpene and phenol; (6) aliphatic petroleum hydrocarbon resins having aBall and Ring softening point of from about 70 to about 135° C.; thelatter resins resulting from the polymerization of monomers consistingof primarily of olefins and diolefins; also included are thehydrogenated aliphatic petroleum hydrocarbon resins; (7) alicyclicpetroleum hydrocarbon resins and the hydrogenated derivatives thereof;and (8) aliphatic/aromatic or cycloaliphatic/aromatic copolymers andtheir hydrogenated derivatives. The desirability and selection of theparticular tackifiers can depend upon the compatibility with othercomponents in the barrier film formulations. When present, theencapsulant compositions of the invention will typically comprise thetackifier in amounts of less than about 80 wt %, typically from about 10to about 65 wt % based on the total weight of the encapsulant, notaccounting for any solvent.

Suitable waxes compatible to PIB or polyolefins include petroleum based,conventional wax, natural-based wax, functionalized wax, and polyolefincopolymers. The term petroleum derived wax includes both paraffin andmicrocrystalline waxes having melting points within the range of fromabout 130° F. to about 225° F. as well as synthetic waxes such as lowmolecular weight polyethylene or Fisher-Tropsch waxes. Most preferredare polyethylene or Fisher-Tropsch waxes with a melting point of atleast about 175° F. Amounts of wax necessary to achieve the desiredproperties will typically range from about 0.5 to about 10 wt % of awax, based on the total weight of the encapsulant, not accounting forsolvent.

A non-limiting example of oils include paraffinic and naphthenicpetroleum oil, highly refined technical grade white petroleum mineraloils such as Kaydol oil from Crompton-Witco and naphthenic petroleum oilsuch as Calsol 5550 from Calumet Lubricants. Diluent can also be aliquid tackifier (having a Ring and Ball softening point below about 25°C.), synthetic liquid oligomer, and mixtures thereof. When present, theformulations of the invention will typically comprise the oil diluent inamounts of less than about 50 wt % based on the total weight of theencapsulant, not accounting for solvent.

The curable encapsulant may optionally comprise additives includingthermal stabilizers, antioxidants, UV absorbers, and hindered aminelight stabilizers. Any known thermal stabilizer may be suitable, andpreferred general classes of thermal stabilizers include, but are notlimited to, phenolic antioxidants, alkylated monophenols,alkylthiomethylphenols, hydroquinones, alkylated hydroquinones,tocopherols, hydroxylated thiodiphenyl ethers, alkylidenebisphenols, O-,N- and S-benzyl compounds, hydroxybenzylated malonates, aromatichydroxybenzyl compounds, triazine compounds, aminic antioxidants, arylamines, diaryl amines, polyaryl amines, acylaminophenols, oxamides,metal deactivators, phosphites, phosphonites, benzylphosphonates,ascorbic acid (vitamin C), hydroxylamines, nitrones, thiosynergists,benzofuranones, indolinones, and the like, and mixtures thereof. Use ofa thermal stabilizer is optional and in some instances is not preferred,especially if it reacts and degrades the active organic component withinthe electronic device. When thermal stabilizers are used, they may bepresent at a level of about 0.00005 wt % and up to about 10 wt % basedon the total weight of the encapsulant, not accounting for solvent.

Any known UV absorber may be suitable for use in the encapsulantcomposition, and preferred general classes of UV absorbers include, butare not limited to, benzotriazole derivatives, hydroxybenzophenones,hydroxyphenyl triazines, esters of substituted and unsubstituted benzoicacids, and the like and mixtures thereof. Hindered amine lightstabilizers (HALS) can be used and are also well known in the art.Generally, hindered amine light stabilizers are secondary, tertiary,acetylated, N-hydrocarbyloxy substituted, hydroxyl-substitutedN-hydrocarbyloxy substituted, or other substituted cyclic amines whichare characterized by a substantial amount of steric hindrance, generallyderived from aliphatic substitution on the carbon atoms adjacent to theamine function. Use of a UV absorber is optional and in some instancesis not preferred, especially if it reacts and degrades active organiccomponent within the electronic device. When UV absorbers are utilized,they may be present in the formulation at a level of about 0.00005 wt %and up to about 10 wt % based on the total weight of the curableencapsulant, not accounting for solvent.

Examples of silane coupling agents that are useful in the encapsulantcomposition include, but are not limited to, C3-C24 alkyltrialkoxysilane, (meth)acryloxypropyltrialkoxysilane,chloropropylmethoxysilane, vinylthmethoxysilane, vinylthethoxysilane,vinyltrismethoxyethoxysilane, vinylbenzylpropylthmethoxysilane,aminopropyltrimethoxysilane, vinylthacetoxysilane,glycidoxypropyltrialkoxysilane,beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,mercaptopropylmethoxysilane, aminopropyltrialkoxysilane, and mixtures oftwo or more thereof. Use of a silane coupling agents is optional and insome instances is not preferred, especially if it reacts and degradesactive organic component within the electronic device. When silanecoupling agents are utilized, they may be present in the formulation ata level of about 0.01 wt % and up to about 10 wt % based on the totalweight of the curable encapsulant, not accounting for solvent.

Other additives conventionally used in pressure sensitive adhesives tosatisfy different properties and meet specific application requirementsalso may be added to the curable encapsulant. Such additives include,but are not limited to, pigments, flow modifiers, dyestuffs, which maybe incorporated in minor or larger amounts into the encapsulantcomposition, depending on the purpose.

The curable encapsulant films can be delivered as sheets or in rolls onsubstrates such as PET, glass, etc.; or between carrier films, such assilicone PET or Kraft paper release liners. The sheets or rollscomprising the encapsulant films may be produced by any suitableprocess. For example, the sheets may be formed by solution casting ordip coating. Solution casting is prepared using techniques known in theart. Typically, the encapsulant components are all dissolved in asolvent or a mixture of solvents e.g., xylene, toluene, heptane, hexane,cyclohexane, and the like, to form a solution. The solution is cast as afilm with a specified weight per square meter, and the solvent is thenlet evaporate to form the solid encapsulant film. Preferred processesare hot melt film extruding, compression molding, injection molding,lamination, blown film processes, tandem extrusion coating, hot meltextrusion casting, melt coextrusion casting, or any suitable meltprocesses known to those of skill in the art. The hot melts are preparedusing techniques known in the art. Typically, the hot melt is preparedby blending the components in the melt at a temperature of about 50-190°C. until a homogeneous blend is obtained, generally about two hours. Theblending temperature should be kept as low as possible to avoidpremature cross-linking and is depended on specific formulations andcomponents, especially if the encapsulant compositions are heat curable.Various methods of blending are known in the art and any method thatproduces a homogeneous blend is satisfactory. During the hot melt filmcoating process, the temperature of the hot melt should be maintainedbelow 150° C. to avoid premature cross-linking or decomposition. In somefilm extrusion processes, the temperature of the hot melt is held at orbelow about 120° C., 110° C. or even below 100° C.

The curable encapsulants are coated in between two liners to formcurable encapsulant free films that have pressure sensitive adhesiveproperties. The curable encapsulant have a Brookfield viscosity range offrom about 10,000 to about 900,000 cps at the coating temperature,typically in the ranges of about 50 to about 200° C., preferably 10,000to 500,000 cps from about 100 to about 130° C. Such viscosity rangesallow the encapsulant to be hot melt coat-able into films. The filmthickness ranges from about 0.01 mm to about 10 mm, preferably fromabout 0.03 to about 0.5 mm. The curable encapsulant films remain aspressure sensitive adhesive films at or below 35° C. and with minimalcold flow in storage.

Upon removal of the first liner, the exposed curable encapsulant film islaminated to either the frontsheet or the substrate with pressure.Subsequently, the second liner is removed and the encapsulant film islaminated to the remaining frontsheet or the substrate. In oneembodiment, the curable encapsulant film is laminated to both frontsheet and substrate simultaneously. Heat (ranging from about 50° C. toabout 190° C., preferably from about 80° C. to about 150° C., and/orvacuum can be applied to encourage lamination, and to remove anyentrapped air and to eliminate any voids in between the layers. Inanother embodiment, because organic active components on the substratestart to decompose at temperatures above 120° C., preferred laminatingtemperature ranges below about 120° C., and in some application belowabout 110° C. The curable encapsulant film is then cured by heat or UVirradiation. Heat cure can be completed with temperatures of from about100 to about 190° C. UV cure is completed with UV irradiation rangingfrom about 280 to about 450 nm.

The cured encapsulant film maintains flexibility and resists creep uponlong term exposure to strain. The creep or cold flow can manifest asdelamination failure of the flexible display or thin film photovoltaicwhen it is bent or held vertical in rigid displays or photovoltaic forlong periods.

In one embodiment, the encapsulant film has irregular surfaces on bothsides of the substrate and cover to facilitate deaeration during thelamination process. Irregular surfaces can be created by mechanicallyembossing or by melt fracture during extrusion of the sheets followed byquenching so that surface roughness is retained during handling. Thesurface pattern can be applied to the sheet through well-known, commonart processes. For example, the extruded sheet may be passed over aspecially prepared surface of a die roll positioned in close proximityto the exit of the extruder die. This imparts the desired surfacecharacteristics to one side of the molten polymer exiting the die. Thus,when the surface of such a die roll has minute peaks and valleys, itwill impart a rough surface to the side of the polymer sheet that passesover the roll, and the rough surface will generally conform respectivelyto the valleys and peaks of the roll surface. Such die rolls aredescribed in, e.g., U.S. Pat. No. 4,035,549 and U.S. Patent PublicationNo. 2003/0124296.

In another embodiment, the encapsulant films may be in a single layer orin multilayer form. The term “single layer” refers to sheets that aremade of or that consist essentially of adhesive described in theinvention. When in a multilayer form, the sheet comprises sublayers, andat least one of the sub-layers is made of or consists essentially of theadhesive in the invention, while the other sub-layer(s) may be made ofor comprise any other suitable polymeric material(s), such as, forexample, copolymers of α-olefins and α,β-ethylenically unsaturatedcarboxylic acids (i.e., acid copolymers), partially neutralized ionicacid copolymers (i.e., ionomers), ethylene/vinyl acetate copolymers,polyvinyl acetals) (including acoustic grade polyvinyl acetals),polyurethanes, polyvinylchlorides, polyethylenes (e.g., linear lowdensity polyethylenes), polyolefin block copolymer elastomers,copolymers of α-olefins and α,β-ethylenically unsaturated carboxylicacid esters (e.g., ethylene methyl acrylate copolymers and ethylenebutyl acrylate copolymers), silicone elastomers, epoxy resins, andcombinations of two or more thereof.

Yet in another embodiment, the curable encapsulant described herein isused as encapsulant for photovoltaic cell module. In forming thephotovoltaic cell, the encapsulant sheet or roll, comprising the curableencapsulant in a pressure sensitive adhesive film form, is laminated tothe photovoltaic module assembly. The photovoltaic module assemblyincludes any article or material that can convert light into electricalenergy. Useful photovoltaic cell includes, but are not limited to,wafer-based photovoltaic cells (e.g., c-Si or mc-Si based photovoltaiccells, and thin film photovoltaic cells (e.g., a-Si, c-Si, CdTe, copperindium selenide (CIS), copper-indium-gallium selenide (GIGS), lightabsorbing dyes, or organic semiconductor based solar cells. Within thephotovoltaic module assembly, it is preferred that the cells beelectrically interconnected or arranged in a flat plane. In addition,the photovoltaic module assembly may further comprise electricalwirings, such as cross ribbons and bus bars.

The photovoltaic module/cell ((herein interchangeably used) assembly maybe bifacial. In such embodiments, all the laminating materialspositioned on either side of the photovoltaic cell should besufficiently transparent to allow adequate sunlight or reflectedsunlight to reach the photovoltaic cells. Alternatively, thephotovoltaic cell may have a front sun-facing side (which is alsoreferred to as a front side and, when in actual use conditions,generally faces toward the sun) and a back non-sun-facing side (which isalso referred to as a back side and, when in actual use conditions,generally faces away from the sun). The photovoltaic cells define theboundary between the front and back sides of the photovoltaic cellassembly. In such assembly, all the materials that are present in thelaminate layers positioned in the front sun-facing side of the solarcell assembly should have sufficient transparency to allow adequatesunlight to reach the photovoltaic cells. The materials present in thelaminate layers positioned in the back non-sun-facing side of thephotovoltaic cell layer need not be transparent. The photovoltaic celltypically comprises at least one encapsulant layer comprising theencapsulant, which is laminated to the solar cell assembly. Twocomponents that are “laminated” to each other are bonded either directly(i.e., without any additional material between the two layers) orindirectly (i.e., with additional material, such as interlayer oradhesive materials, between the two layers). In certain laminates, theencapsulant layer comprising the blend composition is directly bonded tothe photovoltaic cell layer.

In one embodiment, the photovoltaic cell assemblies have irregularsurfaces with peaks and voids. Therefore, during the lamination process,the encapsulant sheet comprising the encapsulant will melt and flow overand fill the voids of the photovoltaic cell assembly in a uniformmanner. The thickness of the encapsulant layer, unless otherwisespecified in limited circumstances, is the thickness of the encapsulantlayer prior to lamination. In general, however, the encapsulant layer inthe final photovoltaic module remains at an average total thickness ofabout 1 to about 120 mils (about 0.025 to about 3 mm), preferably about2 to about 40 mils (about 0.05 to about 1 mm).

The photovoltaic cell may further comprise other functional film, sheetlayers, encapsulant layers (e.g., dielectric layers or barrier layers)embedded within the module. Such functional layers may comprise any ofthe above mentioned polymeric films or those that are coated withadditional functional coatings. For example, poly(ethyleneterephthalate) (PET) films coated with a metal oxide coating, such asthose described in U.S. Pat. Nos. 6,521,825 and 6,818,819 and EuropeanPatent No. 1182710, may function as oxygen and moisture barrier layersin the laminates. Additional encapsulant layers comprise other polymericmaterials, such as acid copolymers, ionomers, ethylene/vinyl acetatecopolymers, polyvinyl acetals (including acoustic grade polyvinylacetals), polyurethanes, polyvinyl chlorides, polyethylenes (e.g.,linear low density polyethylenes), polyolefin block copolymerelastomers, copolymers of alpha-olefins and alpha,beta-ethylenicallyunsaturated carboxylic acid esters) (e.g., ethylene methyl acrylatecopolymers and ethylene butyl acrylate copolymers), silicone elastomers,epoxy resins, and combinations of two or more thereof. Suitable filmsfor the incident layer or the backing layer comprise polymers thatinclude but are not limited to, polyesters (e.g., poly(ethyleneterephthalate) and poly(ethylene naphthalate)), polycarbonate,polyolefins (e.g., polypropylene, polyethylene, and cyclic polyolefins),norbornene polymers, polystyrene (e.g., syndiotactic polystyrene),styrene-acrylate copolymers, acrylonithle-styrene copolymers,polysulfones (e.g., polyethersulfone, polysulfone, etc.), nylons,poly(urethanes), acrylics, cellulose acetates (e.g., cellulose acetate,cellulose triacetates, etc.), cellophane, silicones, polyvinylchlorides) (e.g., polyvinyl idene chloride)), fluoropolymers (e.g.,polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene,and ethylene-tetrafluoroethylene copolymers), and combinations of two ormore thereof. The polymeric film may be non-oriented, or uniaxiallyoriented, or biaxially oriented. Specific examples of films that may beused in the photovoltaic cell module outer layers (e.g., the incidentlayer or the backing layer) include, but are not limited to, polyesterfilms (e.g., poly(ethylene terephthalate) films), fluoropolymer films(e.g., Tedlar®), Tefzel®), and Teflon®) films available from DuPont).Metal films, such as aluminum foil, may also be used as the backinglayers. Further the films used in the solar cell module outer layers maybe in the form of multi-layer films, such as afluoropolymer/polyester/fluoropolymer multilayer film (e.g.,Tedlar®)/PET/Tedlar®) or TPT laminate film available from Isovolta AG ofAustria or from Madico of Woburn, Mass.).

In one process, the component layers of the photovoltaic module arestacked in the desired order to form a pre-lamination assembly. Theassembly is then placed into a bag capable of sustaining a vacuum (“avacuum bag”), the air is drawn out of the bag by a vacuum line or othermeans, the bag is sealed while the vacuum is maintained (e.g., at leastabout 27-28 in. Hg (689-711 mm Hg)), and the sealed bag is placed in anautoclave and the pressure is raised to about 150 to about 250 psi(about 11.3 to about 18.8 bar), and a temperature of about 135° C. toabout 180° C., for about 10 to about 50 min. A vacuum ring may besubstituted for the vacuum bag. One type of suitable vacuum bag isdescribed in U.S. Pat. No. 3,311,517. Following the heat and pressurecycle, the air in the autoclave is cooled without adding additional airto maintain pressure in the autoclave. After about 20 min of cooling,the excess air pressure is vented and the laminates are removed from theautoclave. Alternatively, the pre-lamination assembly may be heated inan oven at about 80° C. to about 120° C. for about 20 to about 40 min,and thereafter, the heated assembly may be passed through a set of niprolls so that the air in the void spaces between the individual layersis squeezed out, and the edge of the assembly sealed. The assembly atthis stage is referred to as a pre-press. The pre-press may then beplaced in an air autoclave where the temperature is raised to about 135°C. to about 180° C. at a pressure of about 100 to about 300 psi (about6.9 to about 20.7 bar). These conditions are maintained for about 15 toabout 60 min, after which the air is cooled while no further air isintroduced to the autoclave. After about 20 to about 40 min of cooling,the excess air pressure is vented and the laminated products are removedfrom the autoclave. The photovoltaic cell modules may also be producedthrough non-autoclave processes. Such non-autoclave processes aredescribed, e.g., in U.S. Pat. Nos. 3,234,062; 3,852,136; 4,341,576;4,385,951; 4,398,979; 5,536,347; 5,853,516; 6,342,116; and 5,415,909; inU.S. Patent Publication No. 2004/0182493; in European Patent No. 1235683B1; and in PCT Patent Publication Nos. WO91/01880 and WO03/057478.Generally, the non-autoclave processes include heating thepre-lamination assembly and the application of vacuum, pressure or both.For example, the assembly may be successively passed through heatingovens and nip rolls. (Do we need this paragraph)

In one embodiment, the curable encapsulant film is suitable as anencapsulant for optoelectronic, OLED, photovoltaic cells, organicphotovoltaic cells, flexible thin film organic photovoltaic cells, CIGSphotovoltaic cells, and the like. In one preferred embodiment, theencapsulant is suitable as an encapsulant for organic photovoltaics(OPV), where the moisture and oxygen barrier requirements are mostdemanding. The curable encapsulant film has a number of advantages overconventional liquid encapsulants. The curable encapsulant film describedherein allows the material to fully flow around and over the irregularsurfaces of the photovoltaic cell assembly during laminating process andtherefore minimize air bubbles, and cell breakage. Further, theincorporation of the PIB and fully compatible reactive (meth)acrylicfunctionalized PIB or polyolefin oligomer/polymer delivery high moistureand oxygen barrier properties and the optical clarity of the encapsulantlayer.

In one embodiment, an organic photovoltaic cell with an encapsulantlayer containing no volatile low molecular weight (having a Mw less thanabout 1,000 Da) organic molecule has a higher module efficiency thancells with encapsulant layer containing volatile low molecular weightmolecules. Without wishing to be bound by theory, it is believe thatpresence of such molecules in the encapsulant layers may create voidsupon heating, affect the adhesion between the encapsulant layer and theactive organic layer, and more importantly change the morphology ofactive organic layers because of the migration and solvation of loworganic molecules in the active organic layer. As it is known from“Organic Photovoltaics: Challenges and Opportunities,” by RussellGaudiana, J. of Polymer Science: Part B: Polymer Physics 2012, DOI:10.1002/polb.23083), the morphology of active layer is crucial to themodule efficiency. For example, a high percentage of process time isfocused on controlling the rate of evaporation of the solvent fromactive organic components because it is the major factor in establishingthe optimum morphology of the active layer. The coating quality of theactive layer is determined by the precise thickness, surface roughness,and pinhole-free film as possible.

In another embodiment, the encapsulant layer has a modulus of less thanabout 50×10^4 Pa (Pascals). In one embodiment, the modulus of theencapsulant layer ranges from about 1×10^4 Pa to about 5×10^4 Pa, andpreferably from about 1×10^4 Pa to about 3×10^4 Pa. As electronicdevices demand higher flexibility, lower modulus of the componentsincluding encapsulant layer is desirable.

The following examples are provided to describe the invention in furtherdetail. These examples, which set forth a preferred mode presentlycontemplated for carrying out the invention, are intended to illustrateand not to limit the invention.

EXAMPLES

Components to the Samples are as follows.

Oppanol PIB series and Glassipol series, both from BASF, are PIBs.

PIB diacrylate is a PIB, having a Mw of about 14,000, with a twoterminal acrylates. This was synthesized according to the methoddescribed in T. P. Liao and J. P. Kennedy, Polymer Bulletin, Vol. 6, pp.135-141 (1981).

CN308, from Sartomer, is a reactive polybutadiene diacrylate.

RT2814 and RT2315 from Rextac LLC, are amorphous poly-alpha-olefinhaving a Brookfield viscosity of less than 8,000 cps at 190° C.

Linxar series from Exxon Mobil is a semicrystalline C2-C6 polyolefinswith Mw less than about 100,000 Da, polydispersity index less than about3, and a melting point less than about 100° C.

Irgacure series and Lucirin TPO-L, from BASF, are photoinitiators.

Luperox series from Arkema are thermal initiators.

Trigonox 101 from Akzo Nobel is a thermal initiator.

Escorez 5380 from Exxon Mobil is a tackifier.

SR833S, from Sartomer, is a difunctional acrylate monomer and has amolecular weight of 304 Da.

Viscosity, water vapor transmission rate (WVTR), water take-up, percenttransmittance (% T) refractive index, shear strength, void formation andmodulus of the samples were measured as follows.

Viscosities of some uncured encapsulants were measured using aBrookfield viscometer, spindle 27, at 80° C., 120° C. or 130° C.Viscosities of some Examples were also measured with Rheometer bytemperature sweep at a frequency of 10 rad/s.

Viscosities of some uncured encapsulants were measured by using ARES-MRheometer.

WVTR, water uptake, optical transmittance and refractive index valueswere measured on 18 mil thick cured encapsulant film. The encapsulantwere coated at 130° C., unless otherwise specified, as hot melt, using alab scale hot melt coater, Hot Melt Coater HLC-101 from ChemInstruments,onto a 2-mil silicone release PET (polyethylene terephthalate) liner.The encapsulant film was cured by irradiating with D-bulb (FusionSystems) with a dosage of UVA&B 500-5000 mJ/cm², depending on thesample, or by heating the encapsulant films in an oven at 150-170° C.,depending on the sample. The liner was removed and the tests wereperformed on the 18 mil thick cured encapsulant films.

WVTR was measured with Mocon Permeatran 3/33 at 38° C./100% RH accordingto ASTM F-1249.

Water uptake was measured with Dynamic Vapour Sorption DVS-2000, bySurface Measurement Systems, Ltd.

Optical transmittance (% T) was measured with Perkin Elmer UV/Vispectrometer.

Refractive Index values were measured with ABBE Refractomer by ATAGO.

Shear strength of the cured encapsulant films were measured according toProcedure A, PSTC-107, adapted as follows: (1) the encapsulant wascoated at 5-6 mil thickness as described above on a 2 mil PET barrierfilm, laminated with 2 mil PET release liner, cured as described above,and then conditioned at 23° C. and 50% relative humidity, (2) the shearadhesion was measured under a shear load of 500 g on a 12×25 mm area,applied after wetting out the stainless test panel for 15 min. The shearstrength testing was performed at 23° C. and 50% relative humidity.

For lamination void test, the encapsulants were coated on the 2-milsilicone release PET liner as above at a thickness of about 5-6 mil. Theencapsulant film was transferred from the liner and laminated in betweentwo PET barrier films at 120° C. using XRL 180 Hot Roll Laminator fromWestern Magnum to simulate adhesion onto a device comprising a cover anda substrate. The encapsulant film was cured as noted above. Aftercooling, void (air bubbles) formations were visually examined throughthe PET barrier films.

Example 1

The components of Samples 1-6 are listed in Table 1. All samples wereprepared by mixing the components at 130° C. in a Brabender, or with aGlas-Col, as known to those of skill in the art. For samples 2 and 5,the samples were cooled to 80° C. and the thermal initiators were thenadded. The Brookfield viscosity profile of Sample 4 is shown in FIG. 1.

TABLE 1 Sample (wt % ) Components 1 2 3 4 5 6 Oppanol B15 (M_(w) 75,000)77.0 Oppanol B14 (M_(w) 65,000) 77.0 77.0 Oppanol B13 (M_(w) 60,000)70.0 RT2814 75.0 75.5 PIB diacrylate (M_(w) 14,000) 30.0 CN308 (M_(w)5,000) 24.5 22.5 22.5 22.5 24.5 Irgarcure 819 0.5 0.5 Irgacure 2022 0.5Lucirin TPO-L 1 Luperox 231 0.5 Trigonox 101 0.5 Brookfield viscosity,130° C. 196,000 2,700 450,500 245,000 245,000 2,600 (cps) UV dosage,mJ/cm², 5-6 mil 1000 500 1000 500 Thermal cure, minutes, 150- 10 20 170°C. WVTR at 38° C./100% RH 0.77 4.87 1.12 1.30 1.42 4.53 (g/m² · day)Water take-up, 23° C., 50% RH <100 <100 <100 <100 <100 <100 (PPM) % T,400-110 nm >91% >87% >91% >91% >91% >87% Refractive index n_(D), 25° C.1.525 1.509 1.528 1.528 1.528 1.509 Shear strength, hr, 2.2 psi, SS 7816 135 21 27 17 Lamination voids none none none none none none

The encapsulants of Samples 1-6 were then coated as a film and cured, asset forth above. WVTR was measured at 38° C./100% RH on 18 mil thicknessof pure encapsulant films. Water take-up, % T, refractive index andshear strength was measured on 18 mil cured encapsulant films.

The lamination test indicated no visible voids for the above samples.

Example 2

The components and properties of Sample 4 and Comparative Samples C-1 toC-4 are listed in Table 2. The Comparative Samples C-1 to C-4 wereprepared similarly to the samples in Example 1.

TABLE 2 Samples (wt %) Components 4 C-1 C-2 C-3 C-4 Oppanol B13 (M_(w)60,000) 80.0 77.0 89.5 Oppanol B14 (M_(w) 65,000) 77.0 RT2814 90.0 CN308(M_(w) 5,000) 22.5 14.5 17.5 SR833S (MW 304) 5.0 5.0 10.0 9.5 LucirinTPO-L 0.5 0.5 Irgacure 819 0.5 0.5 Irgacure 2022 0.5 Viscosity* 120° C.(cps) 249,000 189,000 118,000 119,000 9,300 Shear strength Before cure 2min 7 min 4 min 2 min 2 hr (2.2 psi) Shear strength After UV 4.0 hr 8.1hr 6.5 hr 13.1 hr 13.1 hr cured (2.2 psi) Lamination voids none nonenone none none *Viscosity data were from Rheometer.

The addition of low molecular weight SR833S did not negatively affectthe shear strengths or cause voids during lamination at 120° C.,however, the use of encapsulant film formed with low molecular weightmonomers can significantly decrease the performance of the organicelectronic device, often leading to less efficiency.

Example 3

Tackifier was added to comparative formulations C-5 to C-8, listed inTable 3. Comparative Samples C-5 to C-8 were prepared similarly toExample 1 samples.

TABLE 3 wt % Components C-5 C-6 C-7 C-8 C-9 Oppanol B50 (M_(w)  5.0% 3.5% 400,000) Oppanol B10 (M_(w) 31.9% 34.1% 31.4% 36,000) Linxar(M_(w) 90,000, PDI 51.0% 2.4) RT 2814 50.0% Escorez 5380 47.8% 39.8%39.3% 51.1% 58.3% SR833S (MW304) 10.4% 10.0%  9.6% 11.1% 10.1%PIB-diacrylate (M_(w)  4.8%   14,000)     Irgacure 2002  0.2%  0.2% 0.2%  0.2%  0.2% Viscosity* at 120° C. 7,000 2,600 5,400 11,000 4,900(cps) *Viscosity data were from Rheometer.

The viscosities of the comparative samples decreased with the additionof tackifiers, however the addition of low molecular weight monomers candecrease the performance of the organic electronic device.

Example 4

The components to Samples 7-12 are listed in Table 4. The Samples wereprepared similarly to Example 1.

TABLE 4 wt % Components 7 8 9 10 11 Oppanol B15 77.4 34.0 45.0 (M_(w)75,000) Oppanol B12 77.4 (M_(w) 51,000) RT2814, 59.7 wt % RT2315, 19.9wt % Glassipol 54.0 43.0 2300 (MW 2,300) CN308 (M_(w) 22.2 19.9 22.211.5 11.5 5,000) Luperox 0.4 0.5 TBEC Luperox 231 0.5 Luperox 101 0.4Irgacure 819 0.5 Viscosity*, 168,000 20,500 273,000 93,000 250,000 80°C. (cps) Modulus G′, 8.1 × 10⁴ 17.0 × 10⁴ 10.9 × 10⁴ 3.6 × 10⁴ 8.2 × 10⁴30° C. (dyn/cm²) *Viscosity data were from Rheometer.

Samples 7-11 have acceptably low viscosity at 80° C., and thus can becoated or extruded as hot melt and without any solvent even attemperatures of less than 100° C.

In addition to the coat-able viscosity at low temperatures, the lowmodulus values of Samples 7, 10 and 11 (modulus values less than about10×10⁴ dyn/cm²) indicate that these materials are also flexible and softgel-like, which is desirable for some electronic displays.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

We claim:
 1. A curable encapsulant comprising: a) from about 70 to about90 wt % based on the total weight of the curable encapsulant of apolyisobutylene having a Mw of from about 1,000 to about 95,000 Da; b)from about 10 to about 50 wt % based on the total weight of the curableencapsulant of a functionalized polyisobutylene having (i) a Mw of fromabout 1,000 to about 95,000 Da and (ii) greater than one free-radicalreactive functional group per polymer chain, wherein the free-radicalreactive functional group is selected from the group consisting ofterminal (meth)acrylates and/or, terminal acrylates; and c) a freeradical initiator; wherein the curable encapsulant is (i) essentiallyfree of an acrylic monomer with Mw less than about 1,000 Da or volatileorganic compound with Mw less than about 1,000 Da; (ii) essentially freeof a tackifier, and (iii) is a hot melt; and.
 2. A curable encapsulantcomprising: a) from about 70 to about 90 wt % based on the total weightof the curable encapsulant a polyisobutylene having a Mw of from about1,000 to about 95,000 Da; b) from about 10 to about 50 wt % based on thetotal weight of the curable encapsulant a functionalized polyolefinhaving (i) a Mw of from about 1,000 to about 95,000 Da and (ii) greaterthan one free-radical reactive functional group per polymer chain,wherein the free-radical reactive functional group is selected from thegroup consisting of terminal (meth)acrylates and/or, terminal acrylates;and c) a free radical initiator; wherein the curable encapsulant is (i)essentially free of an acrylic monomer with Mw less than about 1,000 Daor volatile organic compound with Mw less than about 1,000 Da; (ii)essentially free of a tackifier, and (iii) is a hot melt.
 3. The curableencapsulant of claim 1 further comprising a functionalized polyolefin,wherein the functionalized polyolefin has (i) a Mw of from about 1,000to about 95,000 Da and (ii) greater than 1 free-radical reactivefunctional group; wherein the free-radical functional group is selectedfrom the group consisting of terminal (meth)acrylates and/or terminalacrylates.
 4. The curable encapsulant of claim 1 further comprising upto 20 wt % of a plurality of desiccant fillers.
 5. The curableencapsulant of claim 2 further comprising up to 20 wt % of a pluralityof desiccant fillers.
 6. The curable encapsulant of claim 1 whichcomprises less than 5,000 ppm of a volatile organic molecule having a Mwless than 1,000 Da.
 7. The curable encapsulant of claim 2 whichcomprises less than 5,000 ppm of a volatile organic molecule having a Mwless than 1,000 Da.
 8. The curable encapsulant of claim 2 wherein thefunctionalized polyolefin is selected from the group consisting of(meth)acrylate-terminated polybutadiene, hydrogenated(meth)acrylate-terminated polybutadiene, and mixtures thereof.
 9. Thecurable encapsulant of claim 1 wherein the modulus of the encapsulantranges from about 1×10^4 to about 50×10^4 dyn/cm² at 30° C.
 10. Thecurable encapsulant of claim 2 wherein the modulus of the encapsulantranges from about 1×10^4 to about 50×10^4 dyn/cm² at 30° C.
 11. Anarticle comprising the curable encapsulant of claim 9 which is anelectronic device.
 12. An article comprising the curable encapsulant ofclaim 10 which is an electronic device.
 13. A method of forming anelectronic device comprising: (1) laminating the curable encapsulant ofclaim 1 on at a first substrate at temperature ranges of from about 80°C. to about 120° C.; (2) applying a second substrate onto theencapsulant; and (3) curing the curable encapsulant with UV irradiationranging from about 280 to about 450 nm or at temperatures from about 100to about 190° C.; whereby the encapsulant adheres the first substrateand the second substrate together.
 14. A method of forming an electronicdevice comprising: (1) laminating the curable encapsulant of claim 2 onat a first substrate at temperature ranges of from about 80° C. to about120° C.; (2) applying a second substrate onto the encapsulant; and (3)curing the curable encapsulant with UV irradiation ranging from about280 to about 450 nm or at temperatures from about 100 to about 190° C.;whereby the encapsulant adheres the first substrate and the secondsubstrate together.